This invention relates to CRT (cathode ray tube) display devices, and more particularly to a CRT display device which can display a message representing the state of an input signal by message displaying means provided in addition to a CRT.
A CRT display device used popularly for a personal computer is of automatic frequency follow-up type, so as to respond to the scanning frequency of the personal computer.
However, the CRT display device may suffer from the following difficulty: That is, let us consider the case where the CRT display device connected to a personal computer having a certain scanning frequency is adjusted so as to correctly display images thereon. When this device is connected to another personal computer different in scanning frequency, sometimes it is impossible for the device to correctly display images, because of the different signal timing. In this case, it is necessary for the user to adjust the horizontal size, horizontal position, vertical size and vertical position of the CRT display device.
FIG. 8 shows an external appearance of one example of a conventional CRT display device of automatic frequency follow-up type.
With the CRT display device 51, the user operates operating switches in a display operating section 53 while watching images displayed on a CRT 52, to adjust the horizontal size, horizontal position, vertical size and vertical position.
FIG. 9 shows essential parts of the display operating section 53.
The horizontal size, horizontal position, vertical size and vertical position can be adjusted by key switches 54, 55, 56 and 57, respectively.
In addition, a key switch 58 is operated to store the horizontal size, horizontal position, vertical size and vertical position in an internal non-volatile memory. The symbol marks provided above the key switches 54 through 57 indicate the adjusting functions of those key switches, respectively.
With the above-described conventional CRT display device 51, the horizontal size, horizontal position, vertical size and vertical position can be adjusted in the case where an image is displayed on the CRT. However, the device suffers from a difficulty that, in the case where no image is displayed on the CRT, it cannot be determined why no image is displayed. More specifically, it cannot be determined which of the following reasons has caused the trouble: no input signal is applied thereto because the CRT display device 51 is insufficiently connected to the personal computer or the like, or an input signal applied to the CRT display device from the personal computer or the like is out of the range of tolerance of the CRT display device 51, or others. Thus, in this case, it is rather difficult to deal with the trouble.